Acute lower respiratory tract infections (LRTIs) account for more than 27% of all hospitalizations among US children under five years of age, with recurrent LRTIs in children a recognized risk factor for asthma. Within rural areas of Montana, Alaska, and the Navajo Reservation, research has shown that residential biomass combustion leads to elevated indoor levels of fine particulate matter (PM2.5) that often exceed current health- based air quality standards. Parallel findings have been observed in several developing countries where biomass combustion is commonly used for cooking and/or heating. This is concerning, as PM2.5 exposure is associated with many adverse health outcomes, including a greater than three-fold increased risk of LRTIs. Currently, there is a global effort to reduce indoor biomass smoke exposures in developing countries through the introduction of improved cookstove technology. Similar evidence-based efforts are warranted in rural and Native American communities in the US that suffer from elevated rates of childhood LRTI and commonly use wood for residential heating. To date, exposure reduction strategies in wood stove homes have been either inconsistently effective or include factors that limit widespread dissemination and continued compliance in rural and economically disadvantaged populations. This proposed project will focus on three unique and underserved study areas that have demonstrated associations between wood smoke exposure and LRTI among children. Within (1) rural mountain valley communities in western Montana, (2) Navajo Nation communities, and (3) Alaska Native communities, we will test the efficacy of two intervention strategies for reducing indoor wood smoke PM2.5 exposures and children's risk LRTI. We will conduct a three-arm randomized placebo-controlled post-only intervention trial in wood stove homes with children less than five years old. Education on best-burn practices and training on the use of simple instruments (i.e., stove thermometers and wood moisture meters) will be introduced as one intervention arm (Tx1). An indoor air filtration unit will be introduced as a second treatment arm (Tx2). Efficacy of each treatment arm in reducing indoor PM2.5 and child LRTI will be evaluated against a placebo arm (Tx3, sham air filters). Tx1 and Tx2 interventions will also be compared for sustainability. The primary outcome will be LRTI incidence among children under five years of age. To allow for detection of exposure and outcome differences within each of the three regions, a sample of 324 homes, or 108 within each study area will be equally assigned to each of the three intervention arms. We anticipate that 486 total children will participate in this proposed five year project. The overall hypothesis is that a low-cost, educational intervention targeting indoor wood smoke PM2.5 exposures will be sustainable, and can reduce children's risk of LRTI in underserved Native and rural communities.